This paper focuses on the dynamic impedance characteristics of long-stator linear synchronous motors used in high-speed maglev systems. Based on field-measured data, the short-time Fourier transform (STFT) technique is employed to extract the time-varying spectral information of impedance. The dynamic changes in impedance during the operation of high-speed maglev long-stator motors are revealed. A qualitative explanation of the measured phenomena is provided through a circuit model. The research results are expected to provide theoretical support for the optimization of stator segments changeover control strategies and fault diagnosis in maglev systems.